Tissues and cells from the different lobes of the prostate of selected inbred strains of mice will be cultivated, in specifically designed chemically defined media, in organ and cell cultures. The roles of peptide and steroid hormones in growth and differentiation and the responses to carcinogens will be studied, in an effort to provide model systems for the study in vitro of prostatic hyperplasia and neoplasia. The mouse strains to be used will be selected from among those in which hypertrophic, hyperplastic, or neoplastic changes are found in aged animals and from strains, the accessory sex organs of which, are known or suspected to be particularly susceptible to hormones or carcinogens.